1. Technical Field
The present disclosure relates to a wafer-level packaging of a plurality of integrated devices, such as, for example, microelectromechanical devices (MEMS) and/or electronic devices. The present disclosure moreover relates to a method for manufacturing said wafer-level packaging.
2. Detailed Description
Within the field of integrated devices there is a desire to reduce the dimensions in order to meet increasingly stringent specifications of miniaturization, in particular in the field of portable apparatuses, such as, for example, smartphones, tablets, or personal digital assistants (PDAs).
In a known way, a MEMS integrated device generally comprises a first body (usually defined as “die”), which includes semiconductor material (in particular silicon), integrating a micromechanical structure, operating, for example, as a sensor for detecting one or more quantities (for example, for providing an accelerometer, or gyroscope, or magnetometer) and generates an electrical quantity that is a function of the quantity to be detected (for example, a capacitive variation, a variation of electrical resistance, etc.). In an equally known way, the die is the result of an operation of sawing, or singulation, of a wafer, where a plurality of elementary devices are simultaneously produced, during the manufacturing method.
A MEMS integrated device further comprises at least one second die including semiconductor material (in particular silicon), integrating at least one electronic component or circuit, designed to be electrically coupled to the micromechanical structure so as to co-operate functionally therewith. Typically, the second die integrates an ASIC (Application-Specific Integrated Circuit), electrically coupled to the micromechanical structure, which has, for example, the function of a circuit for reading the electrical quantity detected by the micromechanical structure in the case where it operates as sensor (for example, for performing operations of amplification and filtering of the electrical quantity detected). The ASIC may moreover have further functions of processing and evaluation of the quantities detected in order to provide integrated systems known as “SiPs” (Systems in Package).
A MEMS integrated device generally includes a package, i.e., a container or casing that surrounds, totally or in part, the dice of the device itself, ensuring protection thereof from external agents and enabling electrical connection thereof to the external environment. The assembly of the MEMS integrated device within the corresponding package is usually defined as a whole as a “chip”, and can, for example, be electrically connected to a printed circuit of an electronic apparatus in which the MEMS integrated device itself is to be used.
In particular, in the case where the micromechanical structure presents deformable elements, for example a beam or a membrane that is to undergo deformation according to the quantity to be detected, the package includes a covering structure, or cap, defining at least one cavity, provided in an area corresponding to said deformable elements, in such a way as to provide an empty space that will ensure freedom of movement thereof and will not alter deformation thereof.
A known package structure, defined as wafer-level package, is particularly advantageous in the case of portable applications in so far as it enables resulting dimensions to be obtained that do not depart significantly from those of the dice that are packaged. In brief, the corresponding packaging technique envisages the use of standard processes of micromanufacture of the dice also for the production of the corresponding package by producing at a wafer level, i.e., prior to the corresponding operation of singulation, also the structures for covering and protection of the dice themselves and the corresponding electrical connections towards the outside world, thus simplifying and rendering uniform the overall manufacturing process.
Electrical connection of the chip, formed as described previously, to a printed circuit of an electronic apparatus in which the MEMS integrated device is to be used is typically obtained by means of solder balls formed on the back of the second die (i.e., on the surface of the second die that is opposite to the one to which the first die is coupled). The solder balls are electrically coupled to conductive pads, which extend in the aforementioned cavity through conductive through holes, which extend throughout the thickness of the second die. In turn, the conductive pads are electrically coupled to respective conductive pads present on the first die so as to be able to acquire electrical signals generated, in use, by the micromechanical structure and/or to control said micromechanical structure.
In the case of micromechanical structures with a membrane or the like (i.e., structures including further or different deformable elements), the necessary presence of a cavity means that a desired reduction of the resulting dimensions of the package is, however, difficult to obtain on account, for example, of the requisites of thickness of the walls of the cavity (which is frequently made of a composite substrate of the BT—bismaleimide triazine—type, having the function of covering structure). Moreover, a marked reduction of the dimensions involves a greater difficulty in the steps of processing of the covering structure that closes the cavity at the top, and bigger problems linked to mismatches in the coefficients of thermal expansion of the materials used.
In general, there consequently arise problems of reliability and stability of performance, as the dimensions of the package decrease, which can jeopardize the usability of the resulting integrated devices.
There is hence felt the desire in the sector to improve and simplify further the techniques of packaging of MEMS integrated devices, in particular for the purposes of containing the dimensions.